"Virus hunting" using radial distance weighted discrimination

Motivated by the challenge of using DNA-seq data to identify viruses in human blood samples, we propose a novel classification algorithm called "Radial Distance Weighted Discrimination" (or Radial DWD). This classifier is designed for binary classification, assuming one class is surrounded by the other class in very diverse radial directions, which is seen to be typical for our virus detection data. This separation of the 2 classes in multiple radial directions naturally motivates the development of Radial DWD. While classical machine learning methods such as the Support Vector Machine and linear Distance Weighted Discrimination can sometimes give reasonable answers for a given data set, their generalizability is severely compromised because of the linear separating boundary. Radial DWD addresses this challenge by using a more appropriate (in this particular case) spherical separating boundary. Simulations show that for appropriate radial contexts, this gives much better generalizability than linear methods, and also much better than conventional kernel based (nonlinear) Support Vector Machines, because the latter methods essentially use much of the information in the data for determining the shape of the separating boundary. The effectiveness of Radial DWD is demonstrated for real virus detection.Comment: Published at http://dx.doi.org/10.1214/15-AOAS869 in the Annals of Applied Statistics (http://www.imstat.org/aoas/) by the Institute of Mathematical Statistics (http://www.imstat.org

Fantastic Behavior of High-TC Superconductor Junctions: Tunable Superconductivity

Carrier injection performed in oxygen-deficient YBa2Cu3O7(YBCO) hetero-structure junctions exhibited tunable resistance that was entirely different with behaviors of semiconductor devices. Tunable superconductivity in YBCO junctions, increasing over 20 K in transition temperature, has achieved by using electric processes. To our knowledge, this is the first observation that intrinsic property of high TC superconductors superconductivity can be adjusted as tunable functional parameters of devices. The fantastic phenomenon caused by carrier injection was discussed based on a proposed charge carrier self-trapping model and BCS theory.Comment: 5 pages, 4 figure

Dynamical excitations in the collision of 2D Bose-Einstein condensates

We carry out simulations of the collision of two components of an adiabatically divided, quasi-2D BEC. We identify under, over and critically damped regimes in the dipole oscillations of the components according to the balance of internal and centre-of-mass (c.m.) energies of the components and investigate the creation of internal excitations. We distinguish the behaviour of this system from previous studies of quasi-1D BEC's. In particular we note that the nature of the internal excitations is only essentially sensitive to an initial phase difference between the components in the overdamped regime.Comment: 17 pages, 9 figure

Simulating quantum transport for a quasi-one-dimensional Bose gas in an optical lattice: the choice of fluctuation modes in the truncated Wigner approximation

We study the effect of quantum fluctuations on the dynamics of a quasi-one-dimensional Bose gas in an optical lattice at zero-temperature using the truncated Wigner approximation with a variety of basis sets for the initial fluctuation modes. The initial spatial distributions of the quantum fluctuations are very different when using a limited number of plane-wave (PW), simple-harmonic-oscillator (SHO) and self-consistently determined Bogoliubov (SCB) modes. The short-time transport properties of the Bose gas, characterized by the phase coherence in the PW basis are distinct from those gained using the SHO and SCB basis. The calculations using the SCB modes predict greater phase decoherence and stronger number fluctuations than the other choices. Furthermore, we observe that the use of PW modes overestimates the extent to which atoms are expelled from the core of the cloud, while the use of the other modes only breaks the cloud structure slightly which is in agreement with the experimental observations [1].Comment: 12 pages, 5 figure

Subdwarf B stars from the common envelope ejection channel

From the canonical binary scenario, the majority of sdBs are produced from low-mass stars with degenerate cores where helium is ignited in a way of flashes. Due to numerical difficulties, the models of produced sdBs are generally constructed from more massive stars with non-degenerate cores, leaving several uncertainties on the exact characteristics of sdB stars. Employing MESA, we systematically studied the characteristics of sdBs produced from the common envelope (CE) ejection channel, and found that the sdB stars produced from the CE ejection channel appear to form two distinct groups on the effective temperature-gravity diagram. One group (the flash-mixing model) almost has no H-rich envelope and crows at the hottest temperature end of the extremely horizontal branch (EHB), while the other group has significant H-rich envelope and spreads over the whole canonical EHB region. The key factor for the dichotomy of the sdB properties is the development of convection during the first helium flash, which is determined by the interior structure of the star after the CE ejection. For a given initial stellar mass and a given core mass at the onset of the CE, if the CE ejection stops early, the star has a relatively massive H-rich envelope, resulting in a canonical sdB generally. The fact of only a few short-orbital-period sdB binaries being in the flash-mixing sdB region and the lack of He-rich sdBs in short-orbital-period binaries indicate that the flash mixing is not very often in the products of the CE ejection. A falling back process after the CE ejection, similar to that happened in nova, is an appropriate way of increasing the envelope mass, then prevents the flash mixing.Comment: accepted by A&A 12 pages, 11 figure

Hidden vortices in a Bose-Einstein condensate in a rotating double-well potential

We study vortex formation in a Bose-Einstein condensate in a rotating double-well potential. Besides the ordinary quantized vortices and elusive ghost vortices, "hidden" vortices are found distributing along the central barrier. These hidden vortices are invisible like ghost vortex but carry angular momentum. Moreover, their core size is not given by the healing length, but is strongly influenced by the external potential. We find that the Feynman's rule can be well satisfied only after including the hidden vortices. There is no critical rotating frequency for the formation of hidden vortex while there is one for the formation of ordinary visible vortices. Hidden vortices can be revealed in the free expansion of the Bose-Einstein condensates. In addition, the hidden vortices in a Bose-Einstein condensate can appear in other external potentials, such as a rotating anisotropic toroidal trap.Comment: 6pages,5figure